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Related Grants-in-Aid for Scientific Research:��FY2005-2007 Grant-in-Aid in Scientific Research (B): “Studies on the bioactive pigments isolated from mammalian secretions”�

2.Introduction of KAKENHI Projects

Science & �

Engineering Chemical studies on the red sweat of the

hippopotamus

Kimiko Hashimoto�Associate Professor�

Kyoto Pharmaceutical University

【Background】�

Some mammals produce colored secre-tion on their skin from various glands. For example, hippopotamus secret red sweat on the whole body surface and ele-phants discharge blue liquid from the tem-poral glands on the sides of the head. In spite of the interesting phenomena, chemi-cal studies of the colored principles had not been performed. We focused on the red sweat of the hippopotamus and isola-ted two unstable pigments, called hipposu-doric acid (red) and norhipposudoric acid (orange), as the responsible compounds to the red coloration (Nature, 2004). Accord-ing to the ancient tradition on the roles of the red sweat for the animal, it is useful to protect the skin from harmful UV light and also prevent infection of microbes from the injured skin. We revealed that the isolated pigments must be medicines

by absorbing UV light and also by having antibiotic properties. ��【Results】�

In fact hippopotamus secretion is original-ly colorless and it becomes reddish within a few minutes after perspiration. It finally turns brown producing polymers of the pigments within a few hours. We were in-terested in the mechanisms of the pig-ments formation. In order to isolate the precursor of the pigments, we collected the colorless sweat just after perspiration and analyzed organic molecules of low molecular mass. We found homogentisic acid of reasonable content. Biogenetic consideration of the hipposudoric acid easily suggests that two molecules of ho-mogentisic acid produce the red pigment by an oxidative coupling. Then, “how are they converted?” was the next problem.

Possible candidates oxidizing the homoge-ntisic acid are oxygen, sunlight, microbe, and enzyme. We found that an enzyme contained in the sweat catalyzed this oxi-dation reaction using oxygen in the air. Additionally, we also performed the chem-ical synthesis of these unstable pigments. ��【Outlook】�

One of the next challenges is the structure determination of the brown polymers. The synthetic pigments should be useful not only for clarifying the polymer struc-ture but also for functional properties and the roles for the animal. Another subject is elucidation of the structure and func-tion of the unique enzyme. We hope that these studies contribute to the progress in chemistry and biology.

Fig. 1: The red sweat of the hippopotamus